There have been many different types and kinds of motor and pump assemblies for removing well fluids from a well. For example reference may be made to the following U.S. Pat. Nos. 4,350,478; 4,477,235; 4,687,054; and 4,815,949. Each one of the above mentioned patent describes a motor for use with a pump for fluid pumping purposes. While such combinations are generally desirable in many applications, the use of such electromechanical devices necessitate periodic replacement. In this regard, conventional replacement techniques have required that well production tubing generally attached to such motor-pump assemblies, be removed from the well in order to replace the motor-pump assembly. Following such repair or replacement, the entire structure of the production tubing and the motor-pump assembly must then be reinstalled in the well. Such repair and replacement procedures are both time consuming and expensive.
Because of the above mentioned problems, several attempts have been made to improve such procedures. In this regard, U.S. Pat. No. 4,350,478 mentioned above describes an improved procedure where a motor-pump assembly is supported from below by a seat attached to the end of the production tubing, thus enabling the assembly to be extracted from the well by raising (and lowering) the assembly within the production tubing of the well. While this method of removing and replacing the motor-pump assembly from a well is desirable, such an assembly would be so unwieldy in length that it would be difficult, if not impossible to transport and install such an assembly using conventional transportation and installation equipment.
Another attempt at solving such problems is disclosed in the above-mentioned U.S. patent application Ser. No. 07/462,833. The motor-pump assembly disclosed in this application has a significantly larger transverse to axial length ratio thus, the disclosed assembly may be readily transported and installed with conventional equipment. As noted in this application however, significant design tradeoffs are involved in developing a motor with sufficient thrust to efficiently and effectively drive a pump for removing fluids from a well.
For example, it is well known that in order for a piston to push liquid out of a cylinder, such as the production tubing of a well, it must operate against the hydrostatic pressure of the fluid within that cylinder. In this regard, the hydrostatic pressure of raising fluids from a shallow well of 300 feet compared to a deep well of 5000 feet for example, are significantly different. Thus, although a given motor-pump assembly may be completely satisfactory for operation in a shallow well, such a given assembly, unless designed for deep well operation, would be completely unacceptable in a deep well.
Therefore, it would be highly desirable to have a new and improved motor-pump assembly that would be universally adaptable for use in both shallow and deep wells.